Rocking synchronizes brain waves during a short nap

Why
do we cradle babies or irresistibly fall asleep in a hammock? Although
such simple behaviors are common across cultures and generations, the
nature of the link between rocking and sleep is poorly understood [1,2].
Here we aimed to demonstrate that swinging can modulate physiological
parameters of human sleep. To this end, we chose to study sleep during
an afternoon nap using polysomnography and EEG spectral analyses. We
show that lying on a slowly rocking bed (0.25 Hz) facilitates the
transition from waking to sleep, and increases the duration of stage N2
sleep. Rocking also induces a sustained boosting of slow oscillations
and spindle activity. It is proposed that sensory stimulation associated
with a swinging motion exerts a synchronizing action in the brain that
reinforces endogenous sleep rhythms. These results thus provide
scientific support to the traditional belief that rocking can soothe our
sleep.